During his visit to the United States this week, Russian President Dmitry Medvedev said that he and U.S. President Barack Obama have so many issues on their agenda that maybe they should consider conducting diplomacy via text message.

Speaking at the Brookings Institution in Washington, Medvedev deadpanned that "it takes too long for messages between Washington and Moscow to be printed and brought to us by our staff."

Medvedev's tongue-in-cheek remark reflected a degree of engagement, cooperation, and comfort between the Russian and American presidents that has not been seen in years.

In the past week alone, Obama and Medvedev have signed a major new arms control treaty, collaborated on a landmark deal to get Ukraine to agree to give up its highly enriched uranium, and worked in concert to help rein in civil unrest in Kyrgyzstan.

The new tone in the relationship, and the concrete deliverables it is producing, are partially a byproduct of the personal chemistry that has developed over the past year between Obama and Medvedev, analysts say.

"Both sides are pursuing their national interests. But the atmosphere is very positive," says Fyodor Lukyanov, the editor in chief of the Moscow-based journal "Russia in Global Affairs." "Obama and Medvedev are both very pragmatic. But they are also both very good-natured people. This helps relations and it helps resolve difficult issues."

Obama and Medvedev have other things in common as well. Both are in their forties and hail from the generation that rose in politics at the end of the Cold War. Both are graduates of elite law schools who later worked as law professors. And both strive to present themselves as tech-savvy 21st century leaders. In public appearances, they seem comfortable and natural in each other's company.

In an interview with ABC News last week, Medvedev called Obama "a thinker" and "a very pleasant man who it's a pleasure to deal with." Obama has praised Medvedev for his "leadership" and his "clarity."

Speaking to reporters in Prague after the two signed a new Strategic Arms Reduction Treaty (START) on April 8, Obama's chief Russia adviser, Michael McFaul, said that establishing a good personal relationship with Medvedev was not the administration's overriding goal at the outset. But the fact that one developed has helped, he said.

"We want to have a substantive relationship with Russia that advances American interests -- security interests, economic interests, and our interest in promoting universal values," McFaul said. "That's the relationship we want with Russia. Putting an adjective like 'friendly' or 'happy' is not the objective of our policy toward Russia. But as it happens, to build a constructive relationship, it helps to have chemistry. And the reverse is also true -- you develop chemistry if you get things done."Friends In High Places

Personal chemistry and friendly gestures between U.S. and Russian leaders are traditions that go back decades.

During the detente period in the 1970s, Richard Nixon got into Leonid Brezhnev's good graces when he gave the car-crazy Soviet leader a Lincoln Continental as a gift. During perestroika, George H.W. Bush and Mikhail Gorbachev enjoyed excellent personal rapport that made the end of the Cold War a relatively smooth affair. Boris Yeltsin repeatedly addressed Bill Clinton as "my friend Bill."

And in his first meeting with Vladimir Putin, U.S. President George W. Bush famously said he looked into the Russian leader's eyes and got “a sense of his soul.”

Nikolas Gvosdev, a professor of national security studies at the U.S. Naval War College in Rhode Island and editor of the blog "The Washington Realist," says the reason personal relationships loom so large in Russian-American relations is that institutional ties between the two countries are historically weak.

"Personalizing the relationship is easier and more attractive in the absence of strong institutional connections between the two countries," Gvosdev says. "You don't have alliance relationship that binds the militaries. You don't have a particularly strong economic relationship. You certainly don't have good feelings toward either country in both legislatures. It's easier in both countries to be anti-American or anti-Russian than it is to be speaking out in favor of a stronger relationship."

Sometimes, as was the case of the elder Bush and Gorbachev, the personal ties contribute to positive policy results. Often -- as with Nixon and Brezhnev as well as with Clinton and Yeltsin -- the results are mixed.

And sometimes, as with George W. Bush and Putin, personal chemistry between leaders goes hand-in-hand with a deteriorating bilateral relationship.

"In the case of Bush and Putin, the main problem was that they had very good personal relations that didn't translate in any way into good relations between the two countries," Lukyanov explains. "It was a paradox. The personal relations were absolutely normal and even warm until the end. And relations between the two states got worse and worse."

But Lukyanov adds that the key variable that was missing in the U.S.-Russian relationship under Putin and Bush -- which appears to be present with Medvedev and Obama -- is trust.

"Bush and Putin liked each other but did not trust each other," Lyukanov says. "At some point, Putin simply stopped believing the United States and Bush, despite their good personal relations. And America completely stopped trusting Putin. Now, there is an understanding that each side can trust the other side's promises."

Cooperative Efforts

Few would have predicted such trust when Obama moved into the White House 15 months ago. The day after Obama's election in November 2008, as other world leaders were congratulating him on his victory, Medvedev instead delivered a broadside, threatening to deploy short-range missiles aimed at Europe in Russia's western exclave of Kaliningrad.

But chemistry between the two developed quickly after they met for the first time at the G-20 summit in London in April 2009 and during Obama's visit to Moscow in July.

When the START treaty appeared threatened by Russia's last-minute effort to exert concessions on U.S. plans to build a missile-defense system in Europe, it was a phone call between Obama and Medvedev that broke the logjam.

In strife-torn Kyrgyzstan, where Russian and the United States both have military bases and compete for political influence, Obama and Medvedev cooperated to secure an agreement for deposed President Kurmanbek Bakiev to leave the country. The Organization for Security and Cooperation in Europe (OSCE) called the move "an important step toward the stabilization of the situation" and "the prevention of a civil war in Kyrgyzstan."

The changed tone is also facilitating cooperation in areas where Washington has long sought Moscow's assistance. Russia is allowing NATO to transport equipment and supplies across its territory to troops in Afghanistan. And Moscow also appears to be coming around on the long-standing U.S. goal of securing UN sanctions to prevent Iran from acquiring nuclear weapons.

White House spokesman Robert Gibbs told reporters at the START signing in Prague that the rapport that has developed between the two leaders should continue to produce dividends in the future.

Obama "genuinely feels like they can sit down and work through a series of issues in a very frank and honest way, that each side is always negotiating in good faith, and that there is a level of confidence and trust that has built up from the two sides working together," Gibbs said. "This is important as we move forward in both multilateral relationships that involve both countries as well as bilateral issues that the two leaders will work through over the course of the next several years."

Putin's 'Old Ways'

Obama's relations with the other member of Russia's ruling tandem, Prime Minister Vladimir Putin, have been less warm. Prior to his July 2009 visit to Moscow, Obama told the Associated Press that he has a good working relationship with Medvedev, but that "Putin has one foot in the old ways of doing business."

The comment led some observers to speculate whether Obama was trying to drive a wedge between Medvedev and Putin, who is widely seen as Russia's most powerful politician.

Steven Pifer, a former State Department official who is now a senior fellow at the Brookings Institution, says such a move is unlikely. "They are probably wise enough to understand that trying to bolster Medvedev versus Putin would be extremely hard to do," Pifer says. "They're dealing with Medvedev because that's the interlocutor that they have in Russia and they have to assume, as I assume, that when Medvedev speaks he is working on the basis of a policy that he has worked out with Putin.”

There are many pitfalls that could derail this fledgling era of good feeling in U.S.-Russian relations, analysts say.

Washington has yet to press Moscow publicly on its spotty human rights record and its backsliding on democracy. Russia still craves a sphere of influence in the former Soviet space, which the United States staunchly opposes. And Russia still opposes U.S. plans for missile defense.

But for now, Pifer says, the relationship is moving in a constructive direction after nearly a decade of drift.

There are still going to be some weaknesses," Pifer says. "One of them of course is economics. We need to be cautious on issues regarding the post-Soviet space, where there are competing interests between Washington and Moscow."